This invention is directed to new and improved antiviral, antitumor immune system enhancing nucleosides and nucleotides.
The immune system is an inherently complex system that serves its host by providing natural resistance and recovery against both pathogens of an external source as well as aberrant "self" cells, i.e. tumor growth. It provides both "natural", i.e. inborn and unchanging, or "acquired", i.e. adaptive immune response.
For the most part the immune system is innocuous to "self." The immune system is able, in most instances, to recognize "self," its host, and differentiate between "self" and non-self. That is the immune system is "self tolerant." In certain instances, however, the immune system does attack its host as if it was foreign resulting in autoimmunity or autoimmune disease or hypersensitivity expressed in the form of allergies, certain forms of kidney disease and the like.
While for the most part an effective and active immune system confers biological advantages for the host, modern medicine has sought in certain instances to repress the immune system because of autoimmunity hypersensitivity in graft or organ transplant and in other instances stimulate the immune system by immunization. It is therefore advantageous in certain intances to attempt to stimulate the immune system against pathogen or tumor attack and other instances to repress the immune system when it becomes self destructive to the host or for organ transplant or the like.
While most molecular entities either synthetic or natural which are known to stimulate the immune system are large molecules such as interferon, poly I:C or large messenger proteins, certain small molecules have also been shown to modulate the immune system as well. Of the small molecular entities the nucleoside 3-deaza-adenosine has been indicated in U.S. Pat. No. 4,309,419 to Walberg, et al., which issued Jan. 5, 1982, as being an inhibitor of the immune response. Other nucleosides, most notably 8-bromoguanosine, 8-mercaptoguanosine and 7-methyl-8-oxoguanosine have been noted as showing stimulation of the immune system.
Certain components of the immune system are cellular in nature while others are humoral, that is they exist free in serum or other body fluids. Adaptive immunity is based upon special properties of lymphocytes. The lymphocyte populations are generally divided between T lymphocytes commonly called T cells and B lymphocytes commonly called B cells. The T lymphocytes undergo a maturation processing in the thymus whereas the B lymphocytes are continuously generated in the bone marrow and are responsible for the production of antibodies. The lymphocytes freely circulate in the blood and from blood gain access to the tissues from which they are collected and recycled back via the lymph systems including the lymph glands and spleen.
Components of the cellular immune mechanisms include macrophages (hereinafter also refered to as MAC's), polymorphonuclear leucocytes commonly called PMN, mast cells and other cellular or molecular entities such as interferon and the like. Further, complements which are a series of proteins present in the serum can be activated by other immune components or directly by pathogens such as bacteria or the like.
Natural killer cells, hereinafter also identified as NK cells, constitute a group of cells which are concerned with natural immunity. These are lymphoid cells which are generally found in at least the young of all mammallian species and can be readily elicited in older animals. They generally exert a selective cytotoxicity against a range of target cells mostly malignant tumor cells.
The B cells produce antibody. Antibodies are a group of proteins of various classes including IgG, IgM, IgA, IgD, IgE. Not all specific antibody classes are present in different animal species. Generally the higher up on the evolutionary chain of animals the more antibody species present with warm blooded mammals generally having a full contingent of the different antibody species. The immune system is capable of modifying certain regions on the antibody proteins allowing the antibody protein to bind with specific antigens of various origins. These include pathogens, parts of pathogens such as cellular wall polysaccharide molecules, large protein or the like, as well as other foreign debris such as pollen and even in autoimmune diseases portions of the host itself. Some antibody production by the B cells is independent of the T cells while other antibody production is T cell dependent.
There are several groups of T cells including helper T cells which stimulate other T cells and B cells for the production of antibody, supressor T cells which modulate the immune response to keep it from overwhelming the host, cytotoxic T cells (CTL's) which are very important against pathogens especially viral pathogens and delayed hypersensitive T cells which are important in attracting and activating a variety of other cells, including the macrophages.
The immune system is important in protecting the host against a variety of pathogens including bacteria, viruses, protozoa, parasitic worms such as flukes, tapeworms and round worms, fungi, and tumor cells of the host which become parasitic on the host. The antiviral activity of the immune system is generally associated with the T cells whereas the natural antitumor ability of the host resides with the macrophages, the natural killer cells, certain non-T and non-B myeloid cells and with certain portions of the complement system.
As is evident, the immune system is a very complex system which is extremely important to the host for protection of the host against outside pathogens as well as against internal aberrant cells. Catastrophic effects to the host can result when pathogens, tumors or the like overwhelm the immune system of the host. It has even been suggested that tumors may have the ability to depress or subvert the hosts immune system. This is supported by the recognition of clinicians that viral and bacteria infections can be a major contributor to the deaths among tumor patients.
In view of the above it is evident that there is a need for new and improved antiviral and antitumor immune enhancing agents.